1. Field of the Invention
The invention relates to the manufacture of mortar or concrete which includes a fly ash containing carbon and an air entraining chemical admixture which is intended to create tiny air voids in the concrete to allow for the expansion of freezing water.
2. Description of the Prior Art
Fly ash from pulverized coal fired boilers is a "pozzolan" long used with cement, sand, gravel, air entraining chemicals and water to make concrete of special handling characteristics, or to reduce the amount of cement required. Boiler operating characteristics generally leave varying amounts of carbon in the fly ash. High carbon fly ash, with a carbon content of over 5%, is generally considered unsatisfactory for use in concrete because it tends to lower air entrainment. The small air bubbles formed in the mixing and then retained for several hours after pouring of the concrete are necessary in most parts of the United States to allow for the expansion of freezing water to counteract freeze/thaw scaling problems.
One way of trying to overcome this problem is to mix in an excess amount of the air entraining agent. Even in this event however another problem arises during transportation of the product.
This problem is that of maintaining air entrainment in the concrete during its travel from the mixer to the final placement. Loss of entrained air could occur even if there is little or no fly ash containing carbon in the mixture but the loss is more serious with high carbon fly ashes.
A search of the prior art has revealed Patent No. 2,880,101 to Ulfstedt relating to the manufacture of steam cured light aggregate concrete by adding burnt magnesia or dolomite. However, the starting materials as well as the end purpose and product in the Ulfstedt patent are different than that of the present invention. Ulfstedt is concerned with the manufacture of lime silica brick which tends to shrink during steam curing. The slow hydrating burnt magnesia which Ulfstedt adds to the concrete mixture is relatively insoluble and would be unsuitable for use in the present invention which requires a soluble alkaline earth oxide which is immediately hydrated in the mix.
Burley U.S. Pat. No. 4,011,094 shows a composition for patching or grouting which includes magnesium oxide or magnesium hydroxide to provide sag resistance.
The following patents disclose the manufacture of light weight concrete by adding calcium oxide per se, calcium oxide in the form of a burnt clinker or as a mixture of calcium oxide and magnesium oxide to the concrete composition:
______________________________________ 3,470,005 3,884,710 3,785,844 3,558,526 ______________________________________
The following patents depict the manufacture of hydraulic cements containing calcium oxide as an additive:
______________________________________ 2,947,643 3,066,031 ______________________________________
The following patents are submitted as of general interest:
______________________________________ 2,250,107 4,047,962 2,476,306 4,101,332 2,517,993 1,006,725 4,018,617 1,343,929 4,108,619 2,502,418 4,038,095 2,836,502 ______________________________________
None of the above listed patents are believed to suggest or disclose the presently claimed invention.